Interpol

Interpol is a Glyphs plugin for real-time variable font interpolation preview. It allows you to visualize and interact with interpolated glyph shapes, detect interpolation kinks, and fix them using automated tools.

Features

• Live Interpolation Preview - See interpolated glyphs in real-time as you edit masters
• Interactive Axis Control - Adjust axis values with sliders or mouse drag
• Kink Detection - Automatically identify problematic interpolation nodes
• Dekink Tool - Fix interpolation kinks with automated ratio synchronization
• Preview Window - View multiple glyphs at once with live interpolation
• Customizable Display - Control what’s visible: fill, outline, nodes, handles, anchors, kinks

Installation

1. Download the Interpol.glyphsPlugin package
2. Double-click to install, or manually copy to:
   • ~/Library/Application Support/Glyphs 3/Plugins/
3. Restart Glyphs

Getting Started

Enabling the Preview

1. Open a variable font with at least 2 masters
2. Go to View → Show Interpol to enable the reporter
3. The palette panel will appear showing axis sliders and a few other controls

The Palette Panel

The palette appears when Interpol is enabled and shows:

Axis Sliders

• Each axis in your font gets a slider
• Drag the slider to change the interpolation position
• Type exact values in the text field
• Play button (▶) - Animate the axis back and forth
• Speed control - Adjust animation speed (0.5x, 1x and 2x)

Axis Assignment (for Mouse Tool)

Two dropdown menus let you assign axes to mouse movements:

• Horizontal Axis - Controlled by left/right mouse drag
• Vertical Axis - Controlled by up/down mouse drag

The Mouse Tool

The Interpol tool allows you to control axis values by dragging the mouse.

1. Select the Interpol tool from the toolbar (keyboard shortcut: A by default)
2. Click and drag in the canvas:
   • Horizontal drag controls the first assigned axis
   • Vertical drag controls the second assigned axis
3. The interpolated preview updates in real-time as you drag

Note: When the tool is active, normal selection and editing are disabled. Switch back to the Select tool (V) to edit.

Display Options Menu

Right-click on the Edit View to access display options:

Preview Options

• Show Fill - Display filled interpolated glyphs

  

• Show Outlines & Nodes - Display on-curve and off-curve points for interpolated glyphs

  

• Show Anchors - Display anchor positions at interpolated locations

  

• Show Kinks - Highlight potential interpolation problems (see Kink Detection)

  

Master Tracking

• Follow Masters - The interpolation preview follows the current master’s location in the design space

  

Layer Dimming

• Dim Master Layer - Reduce opacity of the underlying master layer to see the interpolation preview more clearly

  

Preview Window & Bubble

• Preview Window - Open a floating window showing a filled interpolation preview of the current line in the Edit View

  

• Preview Bubble - Open an interpolation preview bubble which shows up under the current line in the Edit View

  

• Bubble Size - Adjust the size of the hover bubble (25% to 200%)

Space Preview

• Spacebar Shows Interpolation - When enabled, the usual spacebar preview from Glyphs will show the interpolation at the currently selected axis positions for the current line

  

Kink Detection

Visualizing Kinks

When Show Kinks is enabled, Interpol marks problematic nodes:

• Pink indicators - Appear around nodes with interpolation kinks
• Severity-based sizing - Larger, spiky indicators = more severe kinks
• Real-time updates - Indicators update as you adjust interpolation position
• Kink angle - It shows the angle by which the handle differs from its expected collinear path

Kink indicators only appear when the interpolation severity exceeds a threshold, so minor kinks are ignored.

The Dekink Panel

The Dekink panel provides automated tools to fix interpolation kinks by synchronizing point ratios across masters.

Opening the Panel

1. Select one or more smooth on-curve points with kinks
2. Access the panel via right-click and select Dekink Window…

The panel is non-modal - you can keep it open while working in Glyphs.

Panel Controls

Preview Dekink (checkbox)

• When ON: See a live preview of proposed changes (displayed in green by default)
• When OFF: No preview shown

Mode Selection

Manual Control Mode:
Gives you full control over how the dekinking process works.

• Change slider - Balance between moving on-curve points vs off-curve handles

  • Left (On-Curves) - Primarily moves the on-curve point, keeps handles relatively fixed
  • Right (Off-Curves) - Primarily adjusts handles, keeps on-curve point relatively fixed
  • Middle - Balanced approach (default: 15% from left)

• Match Selection (radio button) - Makes the ratios for all other master follow the ratios in the currently selected master

• Average All (radio button) - Calculates the average ratio across all masters and applies it everywhere

• Compensate Curves (checkbox) - When enabled, attempts to preserve the original curve shape by adjusting handle positions and lengths proportionally

Auto (Preserve Shape) Mode:
Automatically finds the best balance between dekinking and preserving the original curve shapes. This mode:

• Analyzes curve shapes using bezier math
• Calculates optimal adjustments to minimize both kinks and shape distortion
• Works well for most cases without manual tuning
• Uses a maximum deviation threshold (25 units) to prevent excessive changes

Selection Counter

Shows how many smooth points are selected and how many have kinks:

• “X points with kinks” - All selected points have kinks
• “X of Y with kinks” - Some selected points have kinks
• “0 with kinks” - None of the selected points need adjustment

Note: The panel automatically filters your selection to only operate on points that actually have kinks.

Apply Dekink Button

Applies the dekinking to all masters. This operation:

• Modifies point positions across all masters
• Can be undone with Edit → Undo (⌘Z)
• Triggers automatic kink re-detection

Dekink Workflow

1. Enable kink visualization: Turn on Show Kinks in the display menu
2. Select problematic nodes: Click nodes marked with pink indicators
3. Open Dekink panel: Right-click on the edit view and select Dekink Window…
4. Choose mode:
   • Try Auto mode first for automatic optimization
   • Use Manual mode if you need specific control
5. Preview: Enable “Preview Dekink” to see changes in green
6. Adjust (Manual mode only):
   • Move the Change slider to balance on-curve vs off-curve movement
   • Toggle Compensate Curves if shape preservation is important
7. Apply: Click “Apply Dekink” to commit changes
8. Verify: Check that kink indicators disappear or become smaller

Settings

Access settings via Window → Interpol Settings...

Available Settings

Tool Keyboard Shortcut

• Default: A
• Change to any single letter key
• Controls which key activates the Interpol mouse tool

Preview Fill Color

• Default: Purple (0.38, 0.0, 0.88, 0.15)
• Color of the filled interpolated shapes

Preview Outline/Nodes/Handles Color

• Default: Black (0.0, 0.0, 0.0, 0.8)
• Color for outline stroke, nodes, and handle lines

Kink Indicator Color

• Default: Pink (1.0, 0.0, 0.6, 1.0)
• Color of the diamond indicators marking kinks

Dekink Window Preview Color

• Default: Green (0.0, 0.7, 0.2, 1.0)
• Color shown when previewing dekink changes

Line Style

• Dotted lines (default) - Outline uses dotted stroke
• Solid lines - Outline uses solid stroke

Resetting to Defaults

Click ”Reset to Defaults” to restore all original settings.

Version: 3.0
Author: José Solé @ Dogray Type Foundry
License: [Your License]